Data:
Data Analysis:
The amount of magnesium oxide was deduced by subtracting the value of crucible + lid from the value of crucible + lid + magnesium oxide.
28.61 grams
-28.48 grams
00.13 grams
If the mass of magnesium oxide was 0.13 grams and the mass of magnesium was 0.09 grams then the mass of oxygen would sum up to 0.04 grams.
00.13 grams
-00.09 grams
00.04 grams
Once the mass of both magnesium and oxygen was known it was easy to calculate the number of moles of magnesium and oxygen in magnesium oxide.
Amount of substance, n = mass (g)
-------------------------------------------
relative atomic mass or molar mass
Magnesium: n = 0.09 grams/ 24 grams
Therefore n = 3.75*10-3 moles
Oxygen: n = 0.04 grams/ 16 grams
Therefore n = 2.5*10-3 moles
To get the empirical formula of magnesium oxide the ratio of oxygen to magnesium can be found by dividing through the smaller number.
Ratio of Oxygen: 2.5*10-3 / 2.5*10-3 = 1
Ratio of Magnesium: 3.75*10-3/ 2.5*10-3 = 1.5
It can therefore be said that for every one atom of oxygen there are 1.5 atoms of magnesium.
However this experiment does not give the most accurate results. The actual formula of magnesium oxide is MgO, which means that for every one atom of oxygen there is only one atom of magnesium. This has been proven theoretically in chart 1.
Error Analysis:
There are many reasons why this experiment didn’t give the exact formula of magnesium oxide.
- Air is about 80% nitrogen. So burning Mg in air results not only in the formation of magnesium oxide, but also a small amount of a "byproduct", magnesium nitride.
- Before starting the experiment the crucibles should have been washed so as to be sure that there were no other particles in it.
- The magnesium could have over burnt and converted into ash, altering the mass of the magnesium oxide or could have burnt less.
Conclusion:
The primary purpose of this experiment was to obtain the empirical fomula of magnesium oxide. This objective was achieved by recording and analyzing appropriate data and coming up with the ratio of oxygen to magnesium. Though the ratio obtained (one atom of oxygen to 1.5 atoms of magnesium) after the experiment was not accurate, it was quite close to the actual formula of magnesium oxide, which is MgO (one atom of oxygen to atom of magnesium).
Evaluation:
The procedure should have stated that the crucibles be washed first and then dried so as to obtain a more accurate mass.
The mass of magnesium oxide was not accurate as some of the magnesium could have burnt and turned into ash.
As there were 4 of us conducting the experiment under time pressure on one could use the fume cupboard, which would mean only one student at a time.
We were given less than two hours to perform the experiment, which meant that we could all do it only once. This was a great disadvantage as there was no time to verify our results by conducting the experiment again.
This was the first practical of the year so I was a bit careless in carrying it out. I should have been more alert while performing the experiment.
Improving the Investigation:
I recommend doing this experiment in a fume cupboard so that any products of the combustion do not escape with the gas as the lid of the crucible is lifted up to let oxygen in. At lest it will stay in one concentrated area and not around the rest of the room where it won't get used at all.
For the experiment to be more accurate the crucibles should be washed before the start of the experiment.
I would also recommend that the experiment topic be given beforehand so that students can research about it and be more aware of what is to be done and do it with as little error as possible.
